Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and an apparatus for transmitting a frame a wireless local area network (WLAN).
Related Art
A wide range of bandwidths from 20 MHz to 160 MHz become available for the existing wireless local area network (WLAN) system. Accordingly, choosing an appropriate channel bandwidth for communications between a transmitting terminal (station (STA)) and a receiving terminal is a determining factor for the performance of the WLAN system.
To choose an appropriate channel bandwidth for communications between transmitting and receiving terminals, a dynamic channel bandwidth setting protocol based on a Request to Send (RTS) frame and a Clear to Send (CTS) frame has been developed for IEEE 802.11ac and subsequent standards. Initial RTS and CTS frames are designed to reduce a hidden node issue and data frame collision overheads. A transmitting terminal transmits an RTS frame to a receiving terminal before transmitting a data frame. The destination terminal, which has received the RTS frame, responds with a CTS frame to the transmitting terminal. Third terminals, which have received the RTS frame and the CTS frame, may delay medium access for a certain period of time in order to protect the data frame to be subsequently transmitted.
According to the dynamic channel bandwidth setting protocol supported by IEEE 802.11ac and subsequent standards, the transmitting terminal transmits the RTS frame via a wide band grater than a channel bandwidth of 20 MHz, and the destination terminal may respond with the CTS frame according to a channel bandwidth currently available for the destination terminal. For example, when the transmitting terminal wishes to use a 160 MHz channel bandwidth, the transmitting terminal transmits the RTS frame through the 160 MHz channel bandwidth. If an 80 MHz channel bandwidth is currently available for the destination terminal, the destination terminal transmits the CTS frame through the 80 MHz channel bandwidth. When the transmitting terminal, which has transmitted the RTS frame, receives the CTS frame through the 80 MHz channel bandwidth, the transmitting terminal needs to transmit a data frame, subsequently transmitted to the target terminal, through a channel bandwidth of 80 MHz or smaller.